Wait, if they're that far inside it's threatened range, then they should have provoked an AO going in... But maybe it wanted them to be closer and unaware, so it could take a full round attack. Also, they should invest in a least one party member with a spot check.

Apparently the wolf wasn't smart enough to use a withdrawal action, nor a five-foot step. Additionally, the troll must have both Combat Reflexes AND 14+ Dexterity for it to use more than one AoO in a single round. Hopefully Eli has Mounted Combat and a high Ride skill so he can negate the damage of that attack.

It was 10 feet inside reach, so it couldn't withdraw, and a 5 foot step wouldn't bring it out of the threatened area.

Also: Combat Reflexes is +dex modifier AOs, so you only need 12, because you still get your base one. Not that 14 dex is a problem because average trolls have 14 anyway. (Though, huge trolls would have 12, assuming 3.5 size advancement and no increases in Dexterity)